Aromatic hydrocarbons constitute a major source of raw material for the production of fuels, industrial solvents, drugs, herbicides, pesticides and plasticisers. The parent hydrocarbons are toxic to most forms of life. In several cases it is known that oxygenated products formed enzymatically from the aromatic hydrocarbon are more harmful than the unsubstituted substrate. Little evidence is available that describes the enzymatic reactions involved in such transformations. The objectives of this research project are to elucidate the mechanisms of oxygen fixation into aromatic hydrocarbons and to define some parameters of biodegradability that relate to the effects of substituents on the benzene nucleus. Pseudomonas putida grows on toluene as sole source of carbon. The enzyme catalyzing the initial oxidation of toluene incorporates two atoms of molecular oxygen into the substrate with the formation of cis-2,3-dihydroxy-1-methylcyclohexa-4,6-diene. This reaction will be investigated in two ways: 1) The enzyme will be purified and the mechanisms of substrate-oxygen-enzyme interaction determined. Techniques to be used include, salt and solvent fractionation, column chromatography, electrophoresis, electron spin resonance, and spectrophotometry. 2) The enzyme is known to oxidize azulene, a model substrate in which electron densities at different positions of the ring are known. Identification and characterization of the products formed by the enzyme will be determined by ultraviolet and infrared spectrophotometry and mass and proton magnetic resonance spectromety. An unidentified Pseudomonas species oxidizes naphthalene to cis-1,2-dihydro-1,2-dihydroxynaphthalene. This enzyme-catalyzed reaction will be investigated in an analogous manner to that described above for toulene. The model substrate of known electron density is 9,10-borazaronaphthalene.